The film begins in the year 1963 with two cowboys, Ennis del Mar and Jack Twist who both find themselves in Signal looking for work. Ennis and Jack meet for the first time at Joe Agguire’s office who sends them on Brokeback mountain to take care of the sheep.
The two young men are strangers at first, with Ennis being shy and withdrawn. They both share their life stories and Jack tells Ennis that he was disowned by his parents while Ennis remained an orphan after his parents died in a car accident.
The two men leave for the mountains with a heard of sheep and they quickly fall into a routine. Slowly, they reveal more things about themselves and about how their families affected them. Jack’s father was a rodeo man but he never taught Jack the trade and Jack resented his father for that. Ennis was raised by his siblings until they got married and then he was forced to take care of himself. Both men went through hard times in the past but their past only made them closer and made them think that there is a connection between them.
After a night of heavy drinking, the two men stumble into their tent and they have sexual intercourse for the first time. The next day, Ennis tells Jack that it will never happen that again but that same night, Ennis goes into Jack’s tent and they have sex again.
One day, Mr. Agguire comes up the mountain to tell Jack that his uncle got sick. A few days later, a snow storm comes even though it is August and Mr. Agguire decides to bring his sheep from the mountain. The two men get into a fight before going down the mountain and they both hit one another.
After they leave the sheep with Mr. Agguire, they both say goodbye to one another and they go their separate ways.
Ennis returns to his sweetheart and they get married. They have two daughters together while living on a farm in the middle of nowhere. Jack participates in rodeos and it is during a rodeo he meets Lureen Newsome and they also end up having a boy of their own.
After four years, Jack sends Ennis a postcard and they agree to meet again. Ennis’s wife sees them kissing outside but tells Ennis nothing about what she saw. Ennis and Jack end up spending a night in a motel and then the next day Ennis tells his wife that he will be gone for a couple of days in the mountains with Jack.
Jack proposes to Ennis that they move together and that they should build for themselves a cabin in the mountains but Ennis refuses, saying that they both have responsibilities and families to take care of. Ennis also tells Jack about two men he used to know and who were homosexuals. The two men were eventually killed and their bodies left to rot in the desert. Jack and Ennis agreed to meet once in a while and go into the mountains to be together. They quickly felt into a routine and while Alma was aware of the fact that her husband was sleeping with another man, she said nothing.
Eventually, Alma files for a divorce and she also has custody of the two girls. When Jack found about Ennis’s divorce, he went quickly to his friend but Ennis turned him away, letting his know that they will no longer be able to continue their relationship as before. As a result, Jack went to Mexico to find a gay prostitute to sleep with.
Alma marries another man and gets pregnant again. Then, during Thanksgiving, Alma confronts Ennis about his relationship with Jack. Ennis gets man and runs away, getting into a fight with another man shortly afterwards. After the incident, Ennis asks Jack if his wife suspects something but he assures Ennis that his wife knows nothing.
Jack and Ennis spend less time together since Ennis has to work constantly to pay child support. Jack lets it slip that he went to Mexico and Ennis figures it out that he went there to find other men to sleep with.
Ennis tries to be with another woman but things don’t work out and he is dumped eventually.
One day, Ennis receives a postcard informing him that Jack has died. Ennis calls Jack’s wife and finds that Jack had a car accident. His body was cremated and half of his ashes were sent to his parents. Ennis goes to visit Jack’s parents and finds among Jack’s clothes one of his old shirts. Jack’s parents give Ennis the shirt and Ennis returns to his hometown.
The film ends with Ennis opening his closet door and looking at Jack’s shirt below a picture of Brokeback mountain.
